The present invention relates to a ceramic substrate used mainly in the semiconductor industry, and particularly to a ceramic substrate that is suitable for a hot plate, an electrostatic chuck, a wafer prober and the like, and is superior in thermal shock resistance, heat uniformity, chuck power and so on.
Semiconductors are very important goods necessary in various industries. A semiconductor chip is produced, for example, by slicing a silicon monocrystal into a predetermined thickness to produce a silicon wafer, and then forming a plurality of integrated circuits and the like on this silicon wafer.
In the process for producing this semiconductor chip, a silicon wafer put on an electrostatic chuck is subjected to various treatments such as etching and CVD to form a conductor circuit, an element and the like. At this time, corrosive gas such as gas for deposition or gas for etching is used; therefore, it is necessary to protect an electrostatic electrode layer from corrosion by these gas. Since it is also necessary to induce adsorption power, the electrostatic electrode layer is usually coated with a ceramic dielectric film and the like.
As this ceramic substrate, Japanese Patent gazette No. 279850 and Japanese Patent gazette No. 2513995, JP Kokai Hei 11-74064 and so on describe electrostatic chucks with a heater which is produced through the process of stacking the green sheets, on which paste of a metal such as tungsten (W) is printed.
However, in ceramic substrates produced by such a process, problems as follows arise: cracks start to be generated at edges of their conductor layer such as a resistance heating element when thermal shock is given to the substrates; or a high temperature area is generated along the resistance heating element.
Furthermore, a scatter is generated in chuck power so that sufficient adsorption power cannot be obtained.
About an internal electrode or a resistance heating element, a leakage current between the electrodes or between the resistance heating elements at high temperature comes into a problem.
The inventors made eager investigations to solve the above-mentioned problems. As a result, the inventors have newly found out that these problems can be solved by making the edge of a cross section of conductor layer constituting an electrostatic electrode, an RF electrode and a resistance heating element into a peaked shape. Thus, the present invention has been made.
Namely, the present invention is a ceramic substrate comprising a conductor layer formed therein, characterized in that a section of the edge of the conductor layer is in a peaked shape.
In the case that the above-mentioned conductor layer in the ceramic substrate of the present invention is a resistance heating element, the present invention functions as a hot plate. In the case that the above-mentioned conductor layer is an electrostatic electrode, the present invention functions as an electrostatic chuck.
In the ceramic substrate, the conductor layer desirably has a portion in the peaked-shape having a width of 0.1 to 200 xcexcm.
The process for producing a ceramic substrate of the present invention is characterized by printing a conductor layer on a ceramic green sheet, integrating the green sheet with another green sheet under heating and pressure, and then sintering the ceramic powder.